NSAIDS (Non-steroidal anti-inflammatory drugs) are used to reduce the pain associated with RA and improve life quality of the patients. These drugs will not, however, put a brake on the RA-associated joint destruction.
Corticosteroids were found to decrease the progression of RA as detected radiographically and are used at low doses to treat part of the RA patients (30 to 60%). Serious side effects, however, are associated with long corticosteroid use (skin thinning, osteoporosis, cataracts, hypertension, and hyperlipidemia).
Synthetic DMARDs (Disease-Modifying Anti-Rheumatic Drugs) (e.g. methotrexate, leflunomide, sulfasalazine) mainly tackle the immuno-inflammatory component of RA. As a main disadvantage, these drugs only have a limited efficacy (joint destruction is only slowed down but not blocked by DMARDs such that disease progression in the long term continues). The lack of efficacy is indicated by the fact that, on average, only 30% of the patients achieve an ACR50 score after 24 months treatment with methotrexate. This means that, according to the American College of Rheumatology, only 30% of the patients do achieve a 50% improvement of their symptoms (O'Dell et al., 1996). In addition, the precise mechanism of action of DMARDs is often unclear.
Biological DMARDs (Infliximab, Etanercept, Adalimumab, Rituximab, Abatacept) are therapeutic proteins that do inactivate cytokines (e.g. TNF-α) or cells (e.g. B-cells or T-cells) that have an important role in the RA pathophysiology (Kremer et al., 2003; Edwards et al., 2004). Although the TNF-α-blockers (Infliximab, Etanercept, Adalimumab) and methotrexate combination therapy is the most effective RA treatment currently available, it is striking that even this therapy only achieves a 50% improvement (ACR50) in disease symptoms in 50-60% of patients after 12 months therapy (St Clair et al., 2004). Some adverse events warnings for anti-TNF-α drugs exist, shedding a light on the side effects associated to this type of drugs. Increased risk for infections (tuberculosis), hematologic events and demyelinating disorders have been described for the TNF-α blockers (see also Gomez-Reino et al., 2003). Besides the serious side effects, the TNF-α blockers do also share the general disadvantages of the biological class of therapeutics, which are the unpleasant way of administration (frequent injections accompanied by infusion site reactions) and the high production cost. Newer agents in late development phase target cytokines such as IL-6, T-cell co-stimulatory molecules and B-cells. The efficacy of these agents is expected to be similar to that of the TNF-α blockers. The fact that a variety of targeted therapies have similar but limited efficacies, suggests that there is a multiplicity of pathogenic factors for RA. This is also indicative for the deficiencies in our understanding of pathogenic events relevant to RA.
The current therapies for RA are not satisfactory due to a limited efficacy (no adequate therapy exists for 30% of the patients). This calls for additional strategies to achieve remission. Remission is required since residual disease bears the risk of progressive joint damage and thus progressive disability. Inhibiting the immuno-inflammatory component of the RA disease, which represents the main target of drugs currently used for RA treatment, does not result in a blockade of joint degradation, the major hallmark of the disease.
US 2005/0009832 describes substituted imidazo[1,2-a]pyrazine-8-yl-amines as modulators of protein kinases, including MAPKAPK5. WO02/056888 describes inhibitors of MAPKAPK5 as TNF modulators able to regulate the expression of certain cytokines. Neither of these prior art references discloses any compound within the scope of the class of compounds described herein below.